Synchronous rectification control circuit, method and flyback switch circuit

Abstract

The present invention provides a synchronous rectification control circuit, a method and a flyback switching circuit. A drive circuit outputs a drive signal to control the turn-on and turn-off of a synchronous rectification transistor; a threshold comparison circuit controls the drive circuit to output a pull-up drive signal to turn on the synchronous rectification transistor when a drain-source voltage is lower than a preset low threshold voltage and controls the drive circuit to output a pull-down drive signal to turn off the synchronous rectification transistor when the drain-source voltage is higher than or equal to a preset high threshold voltage; a voltage regulation control circuit controls the drive circuit to output a drive signal for pulling up a voltage of the drive signal to a preset pull-up voltage high value when the drain-source voltage is lower than a preset voltage regulation reference value.

What is claimed is: 
     
       1. A synchronous rectification control circuit, for controlling a switching circuit having a synchronous rectification transistor, the control circuit comprising:
 a drive circuit, an output end thereof being connected with a driving end of the synchronous rectification transistor, the drive circuit outputting a drive signal to control turn-on and turn-off of the synchronous rectification transistor; 
 a threshold comparison circuit, an input end thereof receiving a drain-source voltage of the synchronous rectification transistor, and wherein when the drain-source voltage is lower than a preset low threshold voltage, a pull-up drive signal is outputted to turn on the synchronous rectification transistor; and when the drain-source voltage is higher than or equal to a preset high threshold voltage, the drive circuit is controlled to output a pull-down drive signal to turn off the synchronous rectification transistor; and 
 a voltage regulation control circuit, collecting the drain-source voltage of the synchronous rectification transistor and comparing the drain-source voltage to a preset voltage regulation reference value, wherein when the drain-source voltage is lower than the preset voltage regulation reference value, the drive circuit is controlled to output a drive signal for pulling up a voltage of the drive signal to a preset pull-up voltage high value, and when the drain-source voltage is higher than or equal to the preset voltage regulation reference value and lower than the preset high threshold voltage, the drive circuit is controlled to enter a voltage regulation state, a voltage of the drive signal is regulated, and the drive signal after being voltage regulated is outputted, such that the drain-source voltage is stable at the preset voltage regulation reference value or around the preset voltage regulation reference value; 
 wherein when turn-on time of the synchronous rectification transistor reaches a certain value or within a certain period before the synchronous rectification transistor is turned off, if the drive circuit does not enter the voltage regulation state, the voltage regulation control circuit outputs a dynamic regulation signal; 
 wherein the control circuit further comprises a dynamic voltage regulation circuit connected with the voltage regulation control circuit; and 
 wherein receiving and responding to the dynamic regulation signal outputted by the voltage regulation control circuit, the dynamic voltage regulation circuit regulates the preset voltage regulation reference value and outputs the preset voltage regulation reference value after being regulated to the voltage regulation control circuit. 
 
     
     
       2. The synchronous rectification control circuit of  claim 1 , wherein the voltage regulation control circuit comprising a recording module for recording a previous turn-on time T 1  of the synchronous rectification transistor, and when the turn-on time of the synchronous rectification transistor is controlled to reach N*T 1 , if the drive circuit does not enter the voltage regulation state, the dynamic regulation signal is outputted, wherein N is a percentage value. 
     
     
       3. The synchronous rectification control circuit of  claim 1 , wherein the voltage regulation control circuit comprises a detection module for detecting time when the drive circuit is in the voltage regulation state. 
     
     
       4. The synchronous rectification control circuit of  claim 3 , further comprising a dynamic voltage regulation circuit connected with the voltage regulation control circuit, and according to the time when the drive circuit is in the voltage regulation state obtained by the detection module, the dynamic voltage regulation circuit regulating the preset voltage regulation reference value to make the time when the drive circuit is in the voltage regulation state equal to or close to a certain value. 
     
     
       5. The synchronous rectification control circuit of  claim 1 , the threshold comparison circuit comprising:
 a first comparator, a negative input end of the first comparator receiving the drain-source voltage outputted by the voltage regulation control circuit, a positive input end of the first comparator being inputted with the preset low threshold voltage, and an output end of the first comparator outputting a first comparison signal; 
 a second comparator, a positive input end of the second comparator receiving the drain-source voltage outputted by the voltage regulation control circuit, a negative input end of the second comparator being inputted with the preset high threshold voltage, and an output end of the second comparator outputting a second comparison signal; and 
 a trigger, receiving the first comparison signal and the second comparison signal, outputting a first control signal and controlling the drive circuit to output the pull-up drive signal when the first comparison signal is at a high level, and outputting a second control signal and controlling the drive circuit to output the pull-down drive signal when the second comparison signal is at a high level. 
 
     
     
       6. A flyback switching circuit comprising the synchronous rectification control circuit according to  claim 1 . 
     
     
       7. A flyback switching circuit comprising the synchronous rectification control circuit according to  claim 2 . 
     
     
       8. A flyback switching circuit comprising the synchronous rectification control circuit according to  claim 3 . 
     
     
       9. A flyback switching circuit comprising the synchronous rectification control circuit according to  claim 4 . 
     
     
       10. A flyback switching circuit comprising the synchronous rectification control circuit according to  claim 5 .